1. Field of the Invention
The present invention relates to a pre-stressed steel and concrete (PSSC) complex girder and particularly, to a PSSC complex girder which can achieve all of the advantages of both a pre-stressed concrete (PSC) girder and a steel girder. The PSSC complex girder can be made by forming a section shape steel structure by joining one or more section shape steel, such as an I-section shape steel or an H-section shape steel disposed either vertically or in parallel. A tensional member is added to compensate for deflection by applying a pre-stress to the section shape steel structure. Concrete is poured into an inner space portion of the section shape steel structure in a predetermined shape.
2. Description of the Background Art
Generally, a pre-stressed concrete beam (hereinafter, a PSC beam) adds tension to a tensional member using hydraulic equipment, after the tensional member is laid inside of a steel reinforcement concrete beam. Both ends of the tensional member extend outside both ends of the beam, and offset tensile stress occurring in a steel reinforcement concrete beam by operating compression having an eccentric distance along the symmetric axis from both ends of the beam.
The tensioning method is divided into a pre-tension method and post-tension method, in accordance with the settling method of the tensional member.
By operation of the tensional member, tensile stress either does not occur, or a very small amount of tensile stress occurs on a lower surface of the PSC beam, which prevents cracks from occurring in the beam. Even if tensile stress occurs on the lower surface of the beam, no cracks occur if the tensile stress is less than the flexural tensile strength. This kind of PSC beam is more variously applied to civil engineering structures, including bridges, than is reinforced concrete (RC).
For example, a bridge having short and medium spans is usually constructed with a PSC beam, while a bridge having long spans is usually constructed with steel materials, but can also be constructed with the PSC beam. In terms of buildings, the PSC beam is used for a built-up structure, which requires a large space.
In the conventional PSC beam, however, there are limitations to a long span and durability because there has been little change in the basic structure of the beam, while there have been changes in settlement devices and hydraulic equipment.
On the other hand, when the strength of a conventional bridge, constructed by girders, is degraded, the chosen construction method for repairing and strengthening the PSC beam with hydraulic equipment, is to fix brackets to both ends of the PSC beam, and fix both ends of tensional member to the brackets with a settlement member.
Such a construction method, however, has problems in management, for example, because the conventional bridge is reinforced when the strength of the bridge is degraded.
In addition, the conventional construction method has disadvantages including corrosion occurring on the lower surface, and the span length becoming shortened because tensile cracks in the concrete occur in the lower flange as a result of partial prestressing.